Field of the Invention
The present invention relates to a motor drive device, particularly, a motor drive device configured to drive a three-phase brushless motor.
Description of the Background Art
A three-phase brushless motor includes: a stator including a plurality of armature coils; a rotor including a plurality of main magnets and rotatably supported; and a position detector configured to output first to third sensor signals each indicating a rotation position of the rotor. The phases of the first to third sensor signals are shifted from one another by 120°. By turning on/off each of a plurality of switching elements in synchronization with the first to third sensor signals to supply drive current to the plurality of armature coils, the rotor can be driven to rotate.
When the rotation of the rotor is locked due to, for example, failure of a load in such a three-phase brushless motor, overcurrent may flow in a switching element to damage the switching element. To address this, Japanese Patent Laying-Open No. 2000-175481 discloses a technique of determining, based on the rotational speed of the rotor, whether or not the rotation of the rotor is locked, and turning off all the switching elements when the rotation of the rotor is locked.